7. CONTACTS FOR DATA PRODUCTION INFORMATION
8. OUTPUT PRODUCTS AND AVAILABILITY
9. DATA ACCESS
10. CONTACTS FOR ARCHIVE/DATA ACCESS INFORMATION
11. REFERENCES
12. RELATED DATA SETS
13. SUMMARY/SAMPLE
14. NOTES
1.1 Parameter/Measurement.
Temperature profiles at 9 layers; precipitable water at 5 layers; surface and tropopause temperature and pressure; and ozone.
1.2 Unit of Measurement.
Temperature in degrees Kelvin (K); precipitable water in centimeters (cm); pressure in millibars (mb); ozone in Dobson Units.
1.3 Data Source.
The main data set used to produce a daily, global description of the ozone, temperature and humidity distributions is that obtained from the analysis of data from the TIROS Operational Vertical Sounder (TOVS) System, flown on the NOAA (National Oceanic and Atmospheric Administration) Operational Polar Orbiting Satellite series (Webowetzki, 1981). The TOVS system consists of three instruments (Kidwell, 1991): the High Resolution Infrared Radiation Sounder (HIRS/2), the Stratospheric Sounding Unit (SSU), and the Microwave Sounding Unit (MSU). The HIRS/2 is a 20 channel infrared spectrometer (along with one visible channel) that makes measurements in the vicinity of 3.7-4.6 micrometers (um), 6.7-11 um and 13-15 um that are sensitive to atmospheric carbon dioxide, water vapor, ozone and the temperature structure of the troposphere. The SSU (supplied by the United Kingdom) is a pressure modulation spectrometer that makes three measurements at the same wavelength in the 15 um carbon dioxide band with different cell pressures to sense the temperature at about 1, 5, and 15 mb in the stratosphere. The MSU is a passive, scanning microwave spectrometer making measurements in four channels in the 5.5 um oxygen band that senses the temperature of the troposphere.
The measurements from the three instruments of the TOVS system are processed by NOAA to produce the TOVS Sounding Product. Contents of this product include: satellite identification, data and Earth-location of observation, solar zenith angle, land/sea indicator, surface (skin) temperature, estimated surface pressure, channels and method used for retrieval, 15 layer temperatures, 3 layer water abundances (precipitable water amount), tropopause temperature and pressure, ozone abundance, cloud cover and top pressure, and sounding radiances (Kidwell, 1991).
1.4 Data Set Identification.
The International Satellite Cloud Climatology Project (ISCCP),
the first project of the World Climate Research Programme, is
organized to obtain global satellite observations of clouds for
research and to produce a cloud climatology covering a period
of at least twelve years. As part of the data analysis, information
concerning the temperature structure and water and ozone abundances
in the atmosphere are used in radiative model analyses of the
satellite radiance measurements to retrieve physical properties
of the surface and clouds (Schiffer and Rossow, 1985). Although
these data are available from the original sources covering a
longer time period, the versions used during the processing of
the satellite data are archived with the cloud climatology.
2.1 Spatial Coverage.
The typical fraction of the globe covered by the TOVS Sounding Product, on a given day within a three hour interval, is 27%. Since the observations are so sparse, no attempt was made to retain information regarding the diurnal variability of temperature and humidity. However, tests of the variability of temperatures in the first layer show that the error associated with neglecting time-of-day is about 2-3 degrees K but is somewhat larger over land. The typical coverage of the globe obtained by collecting all observations from the same day, regardless of time of observation, is about 67%.
2.2 Spatial resolution.
The ISCCP version of the atmospheric data is interpolated to seven layers in the troposphere, defined by a specific surface and tropopause pressure at each location and time, and to two stratospheric temperature layers. The standard pressures defining these layers in the troposphere are 1000, 800, 680, 560, 440, 310, 180, and 50 mb; the stratosphere layers are defined by the pressures 70, 30, and 5 mb. Thus, the layer mean temperatures and humidities represent values at the center pressures of these layers: 900, 740, 620, 500, 375, 245, 115, 50, and 15 mb. The surface and tropopause pressures actually define the extent of the lower and higher layers in the troposphere. For example, if the surface pressure is 900 mb, then the first layer extends from 800 to 900 mb with a center at 850 mb; if the tropopause pressure is 100 mb, then the seventh layer extends from 180 to 100 mb with a center at 140 mb. The two stratosphere layers are fixed regardless of the location of the tropopause.
3.1 Temporal coverage.
The ISCCP atmospheric data are presented as a series of data sets representing daily and complete global coverage, starting 1 July 1983 and running through December 1990.
3.2 Temporal Resolution.
Daily.
4.1 Mission Objectives.
ISCCP focuses on the study of the distribution and variation of cloud radiative properties. Scientific objectives are as follows:
- To produce a global, reduced resolution, infrared and visible, calibrated and normalized radiance data set containing basic information on the radiative properties of the atmosphere from which cloud parameters can be derived.
- To stimulate and coordinate basic research on techniques for inferring the physical properties of clouds from the condensed radiance data set, and to apply the resulting algorithms to derive and validate global cloud climatology for improving the parameterization of clouds in climate models.
- To promote research using ISCCP data and contribute to improved understanding of the Earth's radiation budget (top of atmosphere and surface) and hydrological cycle.
4.2 Key Satellite Flight Parameters.
The NOAA spacecraft are a series of satellites in 870 kilometer (km) (nominal), circular, near-polar, sun-synchronous orbits with an inclination angle of approximately 99 degrees (retrograde) to the equator. They cross the equator during local morning and afternoon (and corresponding night times), with an orbital period of approximately 102 minutes. Each sequential orbit covers adjacent longitudes near the equator and overlapping longitudes near the poles. Temperature sounding and ozone observations are made by the TIROS Operational Vertical Sounder (TOVS) and are used in the ISCCP analysis of B3 data. In addition, the Advanced Very High Resolution Radiometer (AVHRR) on board this series is composed of up to five spectral channels with a nadir resolution of 1.1 km.
4.3 Principles of Operation.
See the TOVS/MSU, TOVS/HIRS, and TOVS/SSU description in the 1991 NOAA Polar Orbiter Data Users Guide (Item 11.1 a). 4.4 Instrument Measurement Geometry.
See the TOVS/MSU, TOVS/HIRS, and TOVS/SSU instrument description in the 1991 NOAA Polar Orbiter Data Users Guide (item 11.1 a).
5.1 Processing Steps and Data Sets.
The TOVS Sounding Product atmospheric data have a resolution of about 2.5 degrees latitude-longitude. The NOAA Geophysical Fluid Dynamic Laboratory (GFDL) data have a resolution of 2.5 degrees latitude and 5 degrees longitude. The ozone climatology has a latitude resolution of 10 degrees. Since the ISCCP 2.5 degree equivalent equal-area grid has lower resolution at higher latitudes than the TOVS Sounding Product, these data are mapped to the ISCCP grid by placing them into the cell which contains the coordinates of the sounding. Only one observation per cell per day is reported. If more than one observation is available, the one closest to the cell-center coordinates is used. The NOAA GFDL and ozone data, having lower resolutions than the ISCCP grid, are mapped such that all ISCCP grid cells with centers within the range of the original data grid cells are filled with same value. Original observations are indicated by an Origin Code value of 1.
To increase the coverage obtained on a single day, grid cells lacking an observation are filled from nearby values, as long as the topographic heights of the two locations differ by no more than one kilometer (actually, the difference is restricted to be < or = 1005.84 meters = 3300 feet - the original units of the topography data set). Synthetic tests of this procedure were conducted to determine the error as a function of the distance over which the observation is moved. In data-dense regions, the observation at one location is compared to nearby observations. The error not only grows with increasing distance but grows more rapidly in the north-south direction than the east-west direction. Based on these results, missing values are filled by nearby observations that are within two grid cells to the east or west, i.e., within a distance of about 500 km. The typical error introduced is expected to be about 2-3 degrees K in temperature and less than 15% for precipitable water and 10% for ozone. With this replication, typical global coverage provided by daily observations is about 85%. Values obtained by replication are indicated by an Origin Code value of 2.
Monthly mean values are formed from the daily TOVS data with spatial replications performed where needed. No value is reported if less than five observations are available during the month. The error produced by replacing a daily observation with the monthly mean value at the same location is about 3 degrees K for temperatures, 17% for water abundances, and 12% for ozone abundances. If no observation is available for a particular location and day and no observation is near enough on that day, then the monthly mean values for that location are used, if available. By filling with the monthly mean values, the daily global coverage is typically about 95%. Monthly mean values used for daily observations are indicated by an Origin Code value of 3.
If a TOVS monthly mean value is not available for a particular location, the ISCCP analysis uses two climatologies to fill in gaps in coverage. These data sets are the NOAA GFDL temperature/humidity climatology (Oort, 1983) and an ozone climatology from the NIMBUS-4 BUV data (Hilsenrath and Schlesinger, 1981). Estimated errors are about 5 degrees K for temperatures, about 25% for water abundances, and about 15% for ozone abundances. Values obtained from the combined climatology are indicated by an Origin Code value of 4.
The differences between the TOVS DAILY and MONTHLY layer-one water abundance show some significant departures from the monthly mean values. Further study of the distribution of these differences with latitude and season reveals a small population (about 2-4%) with values much larger than three standard deviations from the local monthly mean value. Other parameters in the data set did not exhibit this behaviour. These "anomalous" values were removed with the following procedure: (1) distributions of differences between daily and monthly mean, water abundance values for the first three layers in each grid cell are collected for eight latitude zones for each month, (2) a range of variations with respect to the monthly mean is determined by the width of these distributions defined by the plus and minus difference-values with 5% of the mode frequency (approximately equivalent to three standard deviations), (3) daily values outside the range defined by zonal difference distributions and local monthly mean are set equal to the nearest value within the range. Observations which have been changed in this way are indicated by an Origin Code value of 5.
The ISCCP atmospheric data are presented as daily, global maps. The data at a particular location and time are labeled by whether they represent an actual observation at that place and time (Origin Code = 1), nearby observation on the same day (Origin = 2), the TOVS monthly mean observations for that location and month (Origin Code = 3), or the climatological values for that month (Origin Code = 4). Although the typical amount of monthly mean or climatological data used is less than 5%, there are some occasions when fewer TOVS data are used. If data for a whole day are missing, for example, then the values found in the ISCCP data set for that day would be constructed from the TOVS monthly mean and climatological values.
5.2 Derivation Techniques/Algorithms.
See the TOVS/MSU, TOVS/HIRS, and TOVS/SSU description in the 1991 NOAA Polar Orbiter Data Users Guide (item 11.1 a).
5.3 Special Corrections/Adjustments.
See the TOVS/MSU, TOVS/HIRS, and TOVS/SSU description in the 1991 NOAA Polar Orbiter Data Users Guide (item 11.1 a).
5.4 Processing Changes.
This data set has been reprocessed. An error in mapping was found in an earlier version of TOVS atmospheric data delivered to the ISCCP Central Archive (ICA) that affects less than 1% of the grid cells. This error is only noticeable in those temperature values reported for layers with too high a pressure near the edge of high topography regions.
6.1 Data Validation by Producer.
A publication describing the validation of the TOVS data at NOAA/NESDIS (Burdsall, 1991) prior to their use for ISCCP describes quality checking. During this validation all retrievals are checked to see if they are super-adiabatic. All super-adiabatic retrievals are marked as such and are not used for coefficient generation. A final check of the data is made by comparing it to the NMC analysis. If a substantial portion of an orbit is super-adiabatic and differs significantly from the NMC analysis, then the orbit is not distributed nor archived.
6.2 Confidence Level/Accuracy Judgment.
Certain errors are introduced as a result of the processing of the TOVS data. Since the observations are so sparse, no attempt was made to retain information regarding the diurnal variability, resulting in an error of 2-3 degrees K, with somewhat larger errors over land. The error introduced by replacing missing values by nearby observations (within 500 km) is about 2-3 degrees K in temperature, less than 15% in precipitable water and 10% for ozone. The error introduced by replacing daily observations by the monthly mean values is about 3 degrees K for temperature, 17% for precipitable water and 12% for ozone. When the combined climatology data are used to replace the missing TOVS monthly mean value for a particular location, the error introduced is about 5 degrees K for temperature, 25% for precipitable water and 15% for ozone.
6.3 Usage Guidance.
The processing method used in each processing step in Item 5.1 and corresponding error estimates are indicated by the Origin Code which is available for each map cell in the TOVS daily record file.
ISCCP Ice/Snow Data Producer
Dr. William B. Rossow
ISCCP Global Processing Center
NASA Goddard Institute for Space Studies
2880 Broadway
New York, NY 10025
Commercial and FTS: (212) 678-5567
8.1 Tape Products
8.1.1 ISCCP-TOVS
Medium/Specification: Available on 9-track, 6250-bpi tapes.
Format and Content: The data tapes are written in "IBM standard label" format, which means that each data file is preceded and followed by a very small, separate file for documentation purposes. These files contain data set names that can be used to read the data files on some computer systems.
The basic tape characteristics are as follows:
2 Header files on tape in ASCII 2 Ancillary data files on tape in ASCII 1 Ancillary data file on tape in BINARY 12 Climatological data files on tape in BINARY 366 Daily data files on tape in BINARY 13040 Bytes per record in all files
Data Quantity/Rate: One 9-track, 6250-bpi tape/year
Status: Data are available for the period 7/3/83 - 12/31/90.
Plans/Schedule: The NCDS/Goddard Distributed Active Archive Center (DAAC) will continue to support this data set.
8.2 Film Products. None.
8.3 Other Products.
8.3.1 The ISCCP-C2 CD-ROM
Medium/Specification: CD-ROM in ISO 9660 standard.
Format and Content: The data on this disk consist of the ISCCP-C2 data, read routines and associated documentation. The data set includes the variables from the TIROS Operational Vertical Sounder (TOVS) and ISCCP Ice/Snow. Documentation for ISCCP Level C1, ISCCP TOVS, and the ISCCP Ice/Snow data are also included.
Quantity/Rate: 1 CD-ROM disk.
Status: Release date for this product is scheduled for late Spring 1992.
Plans/Schedule: Users interested in this product should contact the NCDS/Goddard DAAC User Support Office for more details.
9.1 Archive Identification
ISCCP Central Archive
NOAA/NESDIS/NCDC
Satellite Data Services Division (SDSD)
Princeton Executive Square, Suite 100
Washington, DC 20233
Commercial and FTS: (301) 763-8400
Telex: RCA 248376 OBSWUR or TRT 197683 KWBC
Commercial and FTS Telefax: (301) 763-8443
NCDS/Goddard DAAC User Support Office
Code 935
NASA/Goddard Space Flight Center
Greenbelt, Maryland 20771
Commercial and FTS: (301) 286-3209
INTERNET: NCDSUSO@NSSDCA.GSFC.NASA.GOV
NSI DECNET: NSSDCA::NCDSUSO
9.2 Procedures for Obtaining Data.
Enquiries about data availability and procedures for acquiring ISCCP-TOVS radiance data should be referred to the ISCCP Central Archive at NOAA/NESDIS. Inquiries for ISCCP/TOVS data from NCDS can be directed to:
NCDS/Goddard DAAC User Support Office
Code 935
NASA/Goddard Space Flight Center
Greenbelt, Maryland 20771
Commercial and FTS: (301) 286-3209
INTERNET: NCDSUSO@NSSDCA.GSFC.NASA.GOV"
NSI DECNET: NSSDCA::NCDSUSO
9.3 NCDS Status/Plans.
The NCDS provides inventory and data access support for the ISCCP-TOVS data.
User Services Branch
Satellite Data Services Division (SDSD)
NOAA/NESDIS/NCDC
Princeton Executive Square, Suite 100
Washington, DC 20233
Commercial and FTS: (301) 763-8400
Telex: RCA 248376 OBSWUR or TRT 197683 KWBC
Commercial and FTS Telefax: (301) 763-8443
Goddard DAAC User Support Office
Code 935
NASA Goddard Space Flight Center
Greenbelt, Maryland 20771
Commercial and FTS: (301) 286-3209
INTERNET: NCDSUSO@NSSDCA.GSFC.NASA.GOV
NSI DECnet: NCF::NCDSUSO
11.1 Satellite/Instrument/Data Processing Documentation
a. Kidwell, K.B., 1991. "NOAA Polar Orbiter Data Users Guide (TIROS-N, NOAA-6, NOAA-7, NOAA-8, NOAA-9 , NOAA-10, NOAA-11, and NOAA-12)." NOAA/NESDIS, U.S. Dept. of Commerce, Washington, DC.
b. Rossow, W.B., L.C. Garder, P-J. Lu and A.W. Walker, 1991. "International Satellite Cloud Climatology Project (ISCCP) Documentation of Cloud Data." WMO/TD No. 266 (revised). World Meteorological Organization, Geneva, 76 pp. plus three appendices.
c. Rossow, W.B. and B. Kachmar, June 1988. "International Satellite Cloud Climatology Project (ISCCP): Description of Atmosphere Data Set." World Meteorological Organization/ International Council of Scientific Unions.
d. Rossow, W.B., E. Kinsella, A. Wolf, L. Garder, July 1985, revised August 1987. "International Satellite Cloud Climatology Project Description of Reduced Resolution Radiance Data." WMO TD-No. 58, World Meteorological Organization/ International Council of Scientific Unions.
e. World Climate Research Programme, November, 1982. "The International Satellite Cloud Climatology Project Preliminary Implementation Plan." World Meteorological Organization. WCP-35.
11.2 Journal Articles and Study Reports
a. Burdsall, E.L, 1991. "NESDIS Operational Sounding Products from Polar Orbiting Satellites." Palaeogeography, Palaeoclimatology, Palaeoecology, 90:107-111
b. Hilsenrath, E., and B.M. Schlesinger, 1981. "Total Ozone Seasonal and Interannual Variations Derived from the 7 Year NIMBUS-4 BUV data set." J. Geophys. Res., 86:12087-12096.
c. London, J.R., B.D. Bojkov, S. Oltmans and J.F. Kelly, 1976. "Atlas of the Global Distribution of Total Ozone, July 1957-July 1967. "Tech. Note NCAR/TN/113 + STR, National Center for Atmospheric Research, Boulder, CO, 276 pp.
d. Masaki, G.T., 1972 (revised 1976). "The Wolf Plotting and Contouring Package." GSFC Computer Program Library #A00227, Computer Science Corp., NASA Goddard Space Flight Center, Greenbelt, MD, 180 pp.
e. Oort, A.H., 1983. "Global Atmospheric Circulation Statistics, 1958-1973." NOAA Professional Paper 14, NOAA Geophysical Fluid Dynamics Laboratory, U.S. Dept. of Commerce, Rockville, MD, 180 pp.
f. Schiffer, R.A., and W.B. Rossow, 1983. "The International Satellite Cloud Climatology Project (ISCCP): The First Project of the World Climate Research Programme," Bull. Amer. Meteor. Soc., 64:779-784.
g. Schiffer, R.A., and W.B. Rossow, 1985. "ISCCP Global Radiance Data Set: A New Resource for Climate Research." Bull. Amer. Meteor. Soc., 66:1498-1505.
h. Werbowetzki, A., (ed.), 1981. "Atmospheric Sounding User's Guide." NOAA, U.S. Dept. of Commerce, Washington, D.C.
11.3 Archive/DBMS Usage Documentation
a. Olsen, L.M, J.W. Closs, and F.E. Corprew, November 1991. "NASA's Climate Data System Primer: Version 4.0." EOS DAAC, NASA Goddard Space Flight Center, Greenbelt, Maryland.
b. World Climate Research Programme, April 1985. "The International Satellite Cloud Climatology Project (ISCCP) -- Catalog of Data and Products." WCP-95.
Because the TOVS data set does not provide complete global coverage at all times, the final atmospheric data set constructed for use in the ISCCP analysis uses two climatologies to fill in gaps in coverage. These data sets are the NOAA GFDL temperature/humidity climatology (Oort, 1983) and an ozone climatology from the NIMBUS-4 BUV data (Hilsenrath and Schlesinger, 1981).
None currently available.
None.